This invention relates to a process for the preparation of organic fluoride compounds, and in particular, to a process for the liquid phase replacement of halogen atoms with fluorine in organic compounds.
A variety of fluorination processes are known wherein fluorine replaces substituents of organic compounds, such as halogn atoms, and the like. Such known processes include both vapor phase fluorination reactions and liquid phase fluorination reactions. Typically, such processes involve the reaction of an organic halide with hydrogen fluoride, sometimes in the presence of catalyst, such as antimony pentafluoride, at atmospheric or super-atmospheric pressures. Many of the known processes, while suitable for laboratory investigations and experiments, are unsuitable for commercial use for various reasons, such as the low purity of product obtained, the high cost of equipment or catalyst which must be employed, or the need for frequent replacement of the catalyst, due to loss or deactivation. One of the common difficulties encountered in vapor phase fluorination reactions results from the highly exothermic nature of such reactions. The heat evolved frequently results in a temperature rise sufficient to cause thermal decomposition of some of the organic substrates and a resultant carbonization of the catalyst. Furthermore, continuous vapor phase processes are often unsuitable for the preparation of product quantities other than high volume since starting the process usually requires precise control and adjustment of conditions which can result in the waste of reactant materials until ideal reaction conditions are achieved.
Some of the problems associated with vapor phase fluorination processes may be avoided through the use of liquid phase fluorination. However, although atmospheric liquid phase processes are known and are used in laboratory preparations, such processes present various difficulties in larger scale commercial applications. For example, it is known that benzotrifluoride can be prepared by the addition of benzotrichloride to liquid anhydrous hydrogen fluoride at atmospheric pressure with the temperature maintained at between about -4.degree. and 19.degree. Celsius. One significant problem with this process is that the reaction rate is relatively slow and therefore the reaction time is in the order of several hours and is undesirably slow for commercial production. Various other liquid phase fluorination processes are known wherein hydrogen fluoride in either gaseous or liquid form is added to a liquid reactant in the presence of a catalyst. Heretofore, the most widely used catalyst for liquid phase fluorination has been antimony pentahalide or a mixture of antimony pentahalide and antimony trihalide. However, antimony halides, and in particular antimony fluorides, although highly effective in the catalysis of fluorination reactions, are relatively expensive materials. To avoid the problems associated with the volatility of hydrogen fluoride, such fluorination reactions are often carried out in closed systems under superatmospheric pressure, necessitating the use of pressure equipment. Thus, although antimony halides provide an effective catalyst for fluorination reactions, a need exists for an effective liquid phase fluorination process that will overcome the aforementioned disadvantages.
It is an object of the present invention to provide an improved process for the liquid phase fluorination of organic halides. It is a further object to provide an improved liquid phase fluorination process wherein the halogen (other than fluorine) on a haloalkyl aromatic compound may be replaced with fluorine under moderate reaction temperatures and at a relatively rapid rate of reaction. It is a still further object to provide an improved liquid phase process for the production of fluoroalkyl aromatic compounds.